1. Field of the Invention
The present invention relates to a thin film magnetic head and to a production process thereof. More particularly it relates to a thin film magnetic head having an upper core with a narrow track width on an inductive head surface facing to a magnetic recording medium, and to a production process thereof.
2. Description of the Related Art
FIGS. 16A and 16B are diagrams each illustrating a conventional thin film magnetic head, in which FIG. 16A is a cross sectional side view of its substantial part, and FIG. 16B is a top view of its upper core layer. FIGS. 17A through 17E are cross sectional side views showing various steps involved in producing a conventional thin film magnetic head. FIGS. 18A and 18B are illustrations of a production process of the conventional thin film magnetic head, in which FIG. 18A is a schematic diagram illustrating a reflection behavior of light exposure at sloping regions in a photolithography step, and FIG. 18B is a top view showing an upper core layer obtained by photolithography. FIGS. 19A and 19B are cross sectional side views of a substantial part of a thin film magnetic head described in U.S. Pat. No. 25,621,596.
An inductive write head for writing magnetic signals on a magnetic recording medium such as a hard disk is laminated on a magnetoresistive read head (MR read head) for reading magnetic signals with the aid of the magnetoresistive effect, at a trailing edge of a slider of a floating type magnetic head facing a magnetic recording medium, and the resultant laminate is used as a composite thin film magnetic head.
In the thin film magnetic head shown in FIG. 16A, a lower core layer 51 of an inductive write head is composed of an Fexe2x80x94Ni alloy (e.g., permalloy) or another highly magnetically permeable material, and serves also as an upper shield layer of an MR read head having an magnetoresistive read element (MR read element) 20. A gap layer 52 of Al2O3 or another nonmagnetic material and is formed to a thickness of Gl on the lower core layer 51.
A first insulation layer 53 of a resist material or another organic resinous material is formed on the gap layer 52 and slopes upward with respect to the top of the gap layer 52. The first insulation layer 53 has a first forward end or apex 53a and a first sloping region 53b extending upward from the first apex 53a, in which the first apex 53a establishes a zero throat height which, in turn, defines a gap depth Gd. A coil layer 54 is composed of Cu or another low-resistance conductive material, and is formed helical in plane on top of the first insulation layer 53.
A second insulation layer 55 of a resist material or another organic resinous material is formed on the first insulation layer 53 so as to cover the coil layer 54, and on the second insulation layer 55 is laminated a third insulation layer 56. The second and third insulation layers 55 and 56 have a second sloped apex 55a and its second sloping region 55b, and a third sloped apex 56a and its third sloping region 56b, respectively. An inclined plane K1 is constituted by the first, second and third sloping regions 53b, 55b and 56b which are formed nearly flush with one another. The inclined plane K1 is set to have a predetermined angle (apex angle) xcex81 with respect to the gap layer 52.
An upper core layer 57 of an Fexe2x80x94Ni alloy (e.g., permalloy) or another magnetic material is formed above the first, second, and third insulation layers 53, 55 and 56, and the gap layer 52. The upper core layer 57 is provided with a narrow tip region 57a, a connecting portion 57b, a body portion 57c, and a back end region (not shown); in which the tip region 57a is connected via the gap layer 52 to the lower core layer 51 on a surface facing a magnetic recording medium; the connecting portion 57b is connected to the tip region 57a in a nearly identical width and is formed on the inclined plane K1; the body portion 57c extends wider from the connecting portion 57b, and covers part of the coil layer 54; and the back end region is magnetically connected via a hole to the lower core layer 51 and is wrapped with the coil layer 54 therearound, which hole is formed in the gap layer 52 and the first insulation layer 53 at a position which is nearly the center of the coil layer 54 (FIG. 16B). A connecting region between the connecting portion 57b and the body portion 57c on the inclined plane K1 is called a pole straight Ps.
A magnetic gap G has a gap length Gl and a gap depth Gd, and the gap length Gl is determined by a distance between the lower core layer 51 and the tip region 57a connected via the gap layer 52, i.e., the thickness of the gap layer 52. The gap depth Gd is determined by a depth of the tip region 57a, that is, a distance between an air bearing surface (ABS) A which is for facing the magnetic recording medium, the left end shown in the figure, and the first apex 53a (zero throat height Z). In a composite thin magnetic head, the lower core layer 51 also serves as an upper shield layer of an MR head, and has a width larger than that of the tip region 57a of the upper core layer 57. A track width Tw is therefore determined by the width of the tip region 57a. 
In the inductive write head configured as above, a recording current is applied to the coil layer 54 and a recording magnetic field is induced to the lower and upper core layers 51 and 57, and magnetic signals are recorded on a magnetic recording medium through a leakage magnetic field, in the air bearing surface (ABS) A, from the magnetic gap G between the lower core layer 51 and the tip region 57a of the upper core layer 57.
Next, a production process of the above conventional thin film magnetic head will be described. Initially, the gap layer 52 having a thickness (gap length) of Gl is formed from Al2O3 or another nonmagnetic material on the lower core layer 51 of an Fexe2x80x94Ni alloy or another magnetic material. The first insulation layer 53 is then formed by lithography using a resist material or another organic resinous material. Subsequently, the resist material slopes, due to its comparatively high viscosity, through heat applied in a heating step for curing the resist material, and thus the first sloping region 53b extending from the first apex 53a is formed (FIG. 17A).
Next, the coil layer 54 helical in plane is formed on the first insulation layer 53, by plating with, for example, Cu (FIG. 17B). The second insulation layer 55 having the second sloping region 55b provided at the second apex 55a is formed on the first insulation layer 53, by photolithography using a resist material or another organic resinous material (FIG. 17C).
On the second insulation layer 55, the third insulation layer 56 having the third sloping region 56b extending upward from the third apex 56a is formed, by photolithography using a resist material or another organic resinous material (FIG. 17D). In the formation of the second and third insulation layers 55 and 56, the first, second and third sloping regions 53b, 55b and 56b are arranged nearly flush with one another to form the inclined plane K1 having the apex angle xcex81.
The upper core layer 57 is then formed by frame plating. Initially, a thin film of a primary coat 58a of the same material with the upper core layer 57, i.e., an Fexe2x80x94Ni alloy or another magnetic material, is formed on the second and third insulation layers 55 and 56, by sputtering or another vacuum film formation technique. A resist material is then coated onto the primary coat 58a to form a photoresist layer 58b (FIG. 17E). The upper core layer 57 is then patterned by exposing the photoresist layer 58b with light from above in the direction indicated by arrows (FIG. 17E), and a film of an Fexe2x80x94Ni alloy or another magnetic material is plated on areas where the primary coat 58a is bared. The residual photoresist layer 58b and unnecessary areas of the primary coat 58a are removed to give the upper core layer 57. The top of the upper core layer 57 is covered by a protective film (not shown) of, for example, Al2O3.
Finally, unnecessary areas of the thin film laminate is removed, and the air bearing surface (ABS) A is formed by lapping, and the gap depth Gd is determined by a distance from the ABS A to the zero throat height Z to give a thin film magnetic head having the inductive head shown in FIG. 16A and 16B.
U.S. Pat. No. 5,621,596 discloses a technique directed to a thin film magnetic head having a shape controlled upper core layer and a production process thereof. According to the technique, a gap layer 62 of a nonmagnetic material is formed on a lower core layer 61 of a highly permeable material, and a first insulation layer 63 of a resist material or another organic resinous material having a first apex 63a is formed on the gap layer 62 (FIG. 19A). The first insulation layer 63 is formed thinner (thickness: 1.5 xcexcm) than conventional equivalents. On the first insulation layer 63, a coil layer 64 of, for instance, Cu is formed helical in plane. A second insulation layer 65 of a resist material or another organic resinous material is laminated on the first insulation layer 63 so as to cover the coil layer 64. The second insulation layer 65 has a second apex 65a at a distance of 3 xcexcm or more toward the ABS A from the first apex 63a, and a second sloping region 65b commencing from the second apex 65a. A third insulation layer 66 of a resist material or another organic resinous material is formed on top of the second insulation layer 65 in a region where the second insulation layer 65 overlies the coil layer 64. An upper core layer 67 of an Fexe2x80x94Ni alloy (e.g., permalloy) or another magnetic material is formed by frame plating on top of the second and third insulation layers 65 and 66.
According to this technique, the second apex 65a establishes a zero throat height Z which defines a gap depth Gd, and the second sloping region 65b defines an apex angle xcex82. A tip region 67a of the upper core layer 67 is formed on the gap layer 62 in the vicinity of the second apex 65a, and a pole straight Ps is provided on the second sloping region 65b. 
In another embodiment of this technique as shown in FIG. 19B, where the second insulation layer 65 covers the coil layer 64, a third apex 66a and a third sloping region 66b define the zero throat height Z and an apex angle xcex82, respectively. The tip region 67a of the upper core layer 67 is formed on top of the second gap layer 62 in the vicinity of the third apex 66a, and the pole straight Ps is provided on the third sloping region 66b. 
According to this technique, the following advantages are to be expected: As the apex angle xcex82 is defined only by the second sloping region 65b (FIG. 19A) or the third sloping region 66b (FIG. 19B), precision in position and angle is increased. In addition, the first insulation layer 63 is formed thinner than conventional equivalents, and the second or third insulation layer 65 or 66 is formed so that the second apex 65a (FIG. 19A) or the third apex 66a (FIG. 19B) is located at a distance of 3 xcexcm or more from the first apex 63a at a distance of 10 xcexcm or more from the commencement of the coil layer 64, thus defining the zero throat height Z. Accordingly, inclination of the top slope in the vicinity of the second apex 65a (FIG. 19A) or the third apex 66a (FIG. 19B) is reduced and the thickness of a photoresist layer (not shown) for patterning the upper core layer 67 is made more uniform, resulting in precise formation of the tip region of the upper core layer 67 by frame plating. Further, as the inclination of the top slope in the vicinity of the second apex 65a (FIG. 19A) or the third apex 66a (FIG. 19B) is reduced, no light will be reflected from the top slope into the tip region 67a and connecting portion 67b, when the body portion 67c is exposed to light for patterning, resulting in the formation of shape controlled upper core layer 67 with high precision. In addition, there is no need of moving the pole straight Ps rearwardly which connects between the connecting portion 67b and the body portion 67c, and thus a thin film magnetic head having high overwrite property can be obtained.
FIGS. 20A and 20B are illustrations of a conventional thin film magnetic head having a plurality of coil layers, in which FIG. 20A is a cross sectional view of its substantial part, and FIG. 20B is a top view of its upper core layer. FIGS. 21A through 21D are cross sectional views of the steps involved in producing the above conventional thin film magnetic head. FIGS. 21A and 21B are cross sectional views of the substantial part of one step of the above production process, in which FIG. 22A is a cross sectional view where a photoresist layer for frame plating is formed, and FIG. 22B is a cross sectional view illustrating the reflection in the light exposure on the photoresist layer.
An inductive write head for writing magnetic signals on a recording medium such as a hard disk is laminated on a magnetoresistive read head (MR read head) the magnetic signals on a trailing edge of a slider of a floating type magnetic head facing to the magnetic recording medium, thus constituting a composite thin film magnetic head.
In the thin film magnetic head shown in FIG. 20A, a lower core layer 51 of an inductive write head also serves as an upper shield layer of an MR read head 20, and is composed of an Fexe2x80x94Ni alloy (e.g., permalloy) or another highly permeable material. A gap layer 52 of Al2O3 or another nonmagnetic material is formed to a thickness of Gl on the lower core layer 51.
A first insulation layer 53 of a resist material or another organic resinous material is formed on the gap layer 52 and is provided with a first apex 53a, a first sloping region 53b extending upward from the first apex 53a with respect to the top of the gap layer 52, and a first plane region 53c being connected to the first sloping region 53b and having a top nearly parallel to the top of the gap layer 52. A first coil layer 54 of copper (Cu) or another low-resistance conductive material helical in plane is formed on top of the first plane region 53c. A second insulation layer 55 of a resist material or another organic resinous material is formed on top of the first insulation layer 53 so as to cover the first coil layer 54. The second insulation layer 55 is provided with a second apex 55a, a second sloping region 55b extending upward from the second apex 55a, and a second plane region 55c being connected to the second sloping region 55b and having a top nearly parallel to the top of the gap layer 52. The second apex 55a is located on the first sloping region 53b, and the second sloping region 55b is arranged nearly flush with the first sloping region 53b. 
A second coil layer 56xe2x80x2 of, for instance, copper (Cu) helical in plane is formed on the second plane region 55c, and a third insulation layer 57xe2x80x2 of a resist material or another organic resinous material is formed on the second insulation layer 55 so as to cover the second coil layer 56xe2x80x2, and is provided with a third apex 57xe2x80x2a, a third sloping region 57xe2x80x2b extending upward from the third apex 57xe2x80x2a, and a third plane region 57xe2x80x2c being connected to the third sloping region 57xe2x80x2b and having a top nearly parallel to the top of the gap layer 52. The third apex 57xe2x80x2a is located on the second sloping region 55b, and the third sloping region 57xe2x80x2b is arranged nearly flush with the second sloping region 55b. 
An upper core layer 58xe2x80x2 of an Fexe2x80x94Ni alloy (e.g., permalloy) or another magnetic material is formed on top of the first, second and third insulation layers 53, 55 and 57xe2x80x2, and the gap layer 52, and is provided with a tip region 58xe2x80x2a, a connecting portion 58xe2x80x2b, a body portion 58xe2x80x2c and a back end region 58xe2x80x2d (FIG. 20B). The tip region 58xe2x80x2a is located on a surface facing a magnetic recording medium, is connected via the gap layer 52 to the lower core layer 51, and has a narrow track width Tw; the connecting portion 58xe2x80x2b is connected to the tip region 58xe2x80x2a in a nearly identical width, and is formed on the first, second and third sloping region 53b, 55b and 57xe2x80x2b; the body portion 58xe2x80x2c extends wider from the connecting portion 58xe2x80x2b and covers part of the first and second coil layers 54 and 56xe2x80x2; and the back end region 58xe2x80x2d is magnetically connected via a hole H to the lower core layer 51 and is wrapped with the first and second coil layers 54 and 56xe2x80x2 therearound. The hole H is formed in the gap layer 52 and the first insulation layer 53 in a position which is nearly the center of the coil layer 54. A connecting region (base region) between the connecting portion 58xe2x80x2b and the body portion 58xe2x80x2c is called pole straight Ps. In this connection, the first and second coil layers 54 and 56xe2x80x2 are formed rounding the back end region 58xe2x80x2d, and only part of these layers are illustrated in FIG. 20A.
A distance between the lower core layer 51 and the tip region 58xe2x80x2a (i.e., the thickness of the gap layer 52) determines the gap length Gl of a magnetic gap G, and a depth of the tip region 58xe2x80x2a, that is, a distance between the air bearing surface (ABS) A which faces the magnetic recording medium and the first apex 53a determines a gap depth Gd. The lower core layer 57xe2x80x2 in such a composite thin film magnetic head also serves as an upper shield layer of the MR head, and is formed wider than the tip region 57xe2x80x2a of the upper core layer 57xe2x80x2. Accordingly, the track width Tw is determined by the width of the tip region 58xe2x80x2a. 
The inductive head having a dual coil layer structure composed of the first and second coil layers 54 and 56xe2x80x2 of the conventional thin film magnetic head is thus configured. A recording current is applied to the first and second coil layers 54 and 56xe2x80x2, and a recording magnetic field is induced to the lower and upper core layers 51 and 58xe2x80x2, and magnetic signals are recorded on a magnetic recording medium through a leakage magnetic field, in the air bearing surface (ABS) A, from the magnetic gap G between the lower core layer 51 and the tip region 58xe2x80x2a of the upper core layer 58xe2x80x2. By configuring the coil layer to have dual layer structure as is described above, a magnetic path can be shortened to improve efficiency in writing, to increase recording density, and to reduce inductance. Such a magnetic head thus obtained is adaptable to recording of high-frequency magnetic signals.
Next, a production process of the above conventional thin film magnetic head will be described. Initially, the gap layer 52 of Al2O3 or another nonmagnetic material is formed to a thickness (gap length) of Gl on the lower core layer 51, which is composed of an Fexe2x80x94Ni alloy or another magnetic material. The first insulation layer 53 is then formed by lithography using a resist material or another organic resinous material. Subsequently, the resist slopes, due to its comparatively high viscosity, through heat applied in a heating step for curing the resist material and thus the first sloping region 53b and the first plane region 53c are formed extending from the first apex 53a (FIG. 21A), which first plane region 53c has a top nearly parallel to the top of the gap layer 52. Separately, the hole H for connecting the upper core layer 58xe2x80x2 to the lower core layer 51 is formed by etching or another technique, which core layer 58xe2x80x2 will be formed in later steps.
Next, the first coil layer 54 is formed helical in plane on the first plane region 53c, by plating with, for example, Cu (FIG. 21B). The second insulation layer 55 is then formed on the first insulation layer 53 so as to cover the first coil layer 54, by applying a resist material or another organic resinous material and subjecting the coated layer to photolithography (FIG. 21C). In this step, the second sloping region 55b extending from the second apex 55a is formed, and an upper area of the second insulation layer 55 constitutes the second plane region 55c nearly parallel to the top of the gap layer 52, as in the first insulation layer 53. The second apex 55a is located on the first sloping region 53b, and the second sloping region 55b is arranged nearly flush with the first sloping region 53b. 
On the second plane region 55c, the second coil layer 54 helical in plane is formed by plating with, for example, Cu. The third insulation layer 57xe2x80x2 is formed on the second insulation layer 55 so as to cover the second coil layer 56xe2x80x2, by photolithography using a resist material or another organic resinous material (FIG. 21D). In this step, the third sloping region 57xe2x80x2b is formed extending upward from the third apex 57xe2x80x2a, and the top of the third insulation layer establishes the third plane region 57xe2x80x2c nearly parallel to the top of the gap layer 52, as in the second insulation layer 55. The third apex 57xe2x80x2a is located on the second sloping region 55b, and the third sloping region 57xe2x80x2b is arranged nearly flush with the second sloping region 55b. 
The upper core layer 58xe2x80x2 is then formed by frame plating. Initially, a thin film of a primary coat 59 of the same material with the upper core layer 58xe2x80x2, i.e., an Fexe2x80x94Ni alloy or another magnetic material (conductive material), is formed at least over the first, second and third insulation layers 53, 55 and 57xe2x80x2 and the gap layer 52, by sputtering or another vacuum film formation technique. A resist material is then spin coated onto the primary layer 59 to form a photoresist layer 60 (FIG. 22A). The upper core layer 58 is then patterned by exposing the photoresist layer 60 with light from above in the direction indicated by arrows in FIG. 22E, and is developed to remove exposed areas of the photoresist layer 60. A film of an Fexe2x80x94Ni alloy or another magnetic material is then plated on areas where the primary coat 59 is bared. The residual photoresist layer 60 and the unnecessary part of the primary coat 59 are removed to give the upper core layer 58xe2x80x2. The top of the upper core layer 58xe2x80x2 is covered by a protective film (not shown) of, for example, Al2O3.
Finally, unnecessary portion of the thin film laminate is removed, and the air bearing surface (ABS) A is formed by lapping, and the gap depth Gd is determined by a distance from the ABS A to the first apex 53a to give a thin film magnetic head having the inductive head shown in FIGS. 20A and 20B. In this connection, the primary coat 59 is integrated with the upper core layer 58xe2x80x2, and is not shown in FIGS. 20A and 20B.
In the conventional thin film magnetic head and its production process shown in FIGS. 16A and 16B, 17A-17E, 18A and 18B, the apex angle xcex81 of the inclined plane K1 constituted by the first, second and third sloping regions 53b, 55b and 56b depends on the positions of the first, second and third apexes 53a, 55a and 56a. The second and third apexes 55a and 56a should therefore be positioned with high precision with respect to the first apex 53a in their formation. Thus, this technique is very complicated.
The apex angle xcex81 is comparatively large in the conventional thin film magnetic head, and a resist material coated in the production process is liable to flow downward. The photoresist layer 58b for the formation of the upper core layer 57 by frame plating becomes thinner in the vicinity of the third sloping region 56b. Accordingly, when the photoresist layer 58b is exposed and developed to form the upper core layer 57 from an Fexe2x80x94Ni alloy or another magnetic material by frame plating, the magnetic material overflows the photoresist layer 58b in the vicinity of the third apex 56a to form an overhang. Thus, the body portion 57c of the upper core layer 57 having desired dimensions cannot be obtained.
Furthermore, as the photoresist layer 58b becomes thicker in the vicinity of the first apex 53a, a focal depth should be deepened or increased in the light exposure step of the photoresist layer 58b for patterning the upper core layer 57 to ensure the tip region 57a and the connecting portion 57b to be patterned with reliability. Such a deep focal depth, however, deteriorates the definition (resolution), and the tip region 57a and the connecting portion 57b cannot be patterned in the vicinity of the first apex 53a with high precision. In particular, a track density increases in recent years with an increasing recording density of magnetic recording media, rendering the size of the tip region 57a in the track width Tw direction to be 1 xcexcm or less. The formation of a target track width Tw controlled with high precision becomes harder and harder.
In patterning of the upper core layer 57 by exposing the photoresist layer 58b with the light, part of exposure light incited from above penetrates the photoresist layer 58b, and is then reflected or diffused on the surface of the primary coat 58a on the inclined plane K1 to expose other areas in addition to the patterned area for the upper core layer 57 (FIG. 18A). Particularly, in a magnetic head having an apex angle xcex81 of 60xc2x0 or more, the light for patterning the body portion 57c of the upper core layer 57 is liable to be reflected on the surface of the primary coat 58a into the tip region 57a. As a result, the pattern of the upper core layer 57 as indicated by a solid line cannot be formed, and, on the contrary, the body portion 57c protrudes toward the tip region 57a and the pole straight Ps is located nearer toward the tip region 57a as indicated by dashed lines (FIG. 18B). Therefore, the photoresist layer is exposed with a broadened track width Tw of the tip region 57a and the connecting portion 57b. A solution to the reflection problem is to move the pole straight Ps toward the back end region (not shown) in order not to affect the track width Tw of the tip region 57a and the connecting portion 57b in the light exposure step of the photoresist layer 58b. 
However, moving the pole straight Ps rearwardly extends the length (pole straight length) P1 from the ABS A to the pole straight Ps longer than the size of the tip region 57a in a direction of the track width Tw, resulting in a reduced flux density at the tip region 57a, which deteriorates the overwrite property of the magnetic head. The over write property is defined in the following manner: When a record is recorded at a low frequency and then overwritten at a high frequency, the degree of decrease of the after-power at this stage of a signal recorded at a low frequency from the output of a signal recorded at low frequency before overwriting at a high frequency defines the overwrite property. The overwrite property is known to be decreased with an increasing pole straight length P1.
According to the conventional thin film magnetic head and the production process thereof, as thus described, the size and shape of the upper core layer 57 is hardly controlled, and a high recording density in magnetic recording media cannot be achieved.
Separately, in the thin film magnetic head shown in FIGS. 19A and 19B and disclosed in the U.S. Pat. No. 5,621,596, the apex angle xcex82 depends on the thickness of the second or third insulation layer 65 or 66, or on the viscosity or other characteristics of the constitutive material thereof such as the resist material or organic resinous material. Therefore, once the material having desired characteristics is selected and the thickness of the second insulation layer 65 (FIG. 19A) or third insulation layer 66 (FIG. 19B) is determined, the apex angle xcex82 is nearly uniquely defined. The apex angle thus defined is hardly changed, which deteriorates the degree of freedom in design of the magnetic head.
The second insulation layer 65 (FIG. 19A) or third insulation layer 66 (FIG. 19B) is formed by application of a resist material or another organic resinous material after the formation of the coil layer 64. The coil layer 64 helical in plane makes a surface to be coated with the material for the second or third insulation uneven, which causes distribution in thickness (unevenness of the surface of the insulation layer) of the formed insulation layer, resulting in deteriorated precision in registration of the zero throat height Z. A solution to the unevenness in thickness of the second or third insulation layer 65 or 66 due to the thickness of the coil layer 64 is to flat and thin the coil layer 64 more than the conventional coil layer 54. The thinned and flatted coil layer 64 increases the overall surface area of the coil layer 64 at the same number of turns with that of the conventional equivalent, and elongates the magnetic path of the upper core layer 67, resulting in an increased inductance and deteriorated high frequency property.
With present day demands for storing and processing a large amounts of data at high density on a magnetic recording medium such as a hard disk, there is a strong felt need for a thin film magnetic head which provides both high recording and processing property and narrow track width. To be more specific, there is a strong need for a thin film magnetic head having a plurality of coil layers as shown in FIGS. 20A and 20B with narrower track width Tw which is defined by the width of the tip region 58xe2x80x2a of the upper core layer 58xe2x80x2. For this purpose, the photoresist layer 60 in an area to be the vicinity of the tip region 58a should be patterned with a particularly high precision.
As the conventional thin film magnetic head shown in FIGS. 20A and 20B, however, has a dual coil layer structure composed of the first and second coil layers 54 and 56, the first, second and third insulation layers 53, 55, and 57xe2x80x2 covering these coil layers have a large overall thickness, and the first, second and third sloping region 53b, 55b, and 57xe2x80x2b formed nearly flush with one another slope upward steeply. When a resist material is spin coated onto the insulation layers for the formation of the photoresist layer 60, which is in turn used for the formation of the upper core layer 58xe2x80x2 by frame plating, the resist material is liable to flow downwards and thereby to have a larger thickness t1 on the gap layer 52 in the vicinity of the first apex 53a, and a smaller thickness t2 on the top of the third insulation layer 57xe2x80x2 where the body portion 58xe2x80x2c is to be formed (FIG. 22A). The thickness t1 in the lower side increases with an increasing viscosity of the resist material, and it will be about 9 to 10 xcexcm when a resist material having a viscosity of about 800 centipoises (cp) is used. The thickness t1 of the photoresist layer 60 is very large, in comparison with that of the upper core layer 58xe2x80x2 to be formed, i.e., about 1 to 2 xcexcm. With such a large thickness t1, the focal depth of an exposure light source in the photolithography step should be increased or deepened, but such an increased focal depth deteriorates the definition (resolution). As a result, the tip region 58xe2x80x2a would not be patterned on the photoresist layer 60 in the vicinity of the first apex 53a with precision, and the tip region 58xe2x80x2a having the desired narrow track width Tw cannot be obtained.
A possible solution to the above problem is to form the photoresist layer 60 with the use of a resist material having a lower viscosity. For example, when a resist material having a viscosity of about 300 cp is used, the thickness t1 on the lower side is reduced to about 6 to 7 xcexcm as indicated by dashed lines in FIG. 22A. However, the thickness t2 on the upper side of the photoresist layer 60 is also reduced to about 1 xcexcm or less, and when the frame plating is conducted using this area of the photoresist layer 60 as a frame for patterning the upper core layer 58 , the plating material (e.g., permalloy) overflows and leaks into the surroundings, which inhibits satisfactory control of the shape of the upper core layer 58xe2x80x2.
Furthermore, the first, second and third sloping region 53b, 55b and 57xe2x80x2b slope upward steeply in the conventional thin film magnetic head, and in patterning of the upper core layer 58xe2x80x2 by exposing the photoresist layer 60 with the light, part of exposure light incited from above penetrates the photoresist layer 60 and then is reflected or diffused on the surface of the primary coat 59 to expose other areas in addition to the patterned areas for patterning the upper core layer 58xe2x80x2 (FIG. 22B). Particularly, in a magnetic head having an apex angle of 45xc2x0 or more in the first, second and third sloping region 53b, 55b and 57xe2x80x2b, the light for patterning the body portion 58xe2x80x2c of the upper core layer 58xe2x80x2 is liable to be reflected on the surface of the primary coat 59 into the tip region 58xe2x80x2a. As a result, the pattern of the upper core layer 58xe2x80x2 as indicated by the solid line cannot be obtained, and, on the contrary, the body portion 58xe2x80x2c protrudes toward the tip region 58xe2x80x2a as indicated by dashed lines (FIG. 20B). Therefore, the photoresist layer is exposed with a broadened track width Tw of the tip region 58xe2x80x2a and the connecting portion 5b, resulting in patterning with a deteriorated precision.
Accordingly, an object of the present invention is to provide a thin film magnetic head having an upper core layer having dimensions controlled with high precision, which can yield high density recording on a magnetic recording medium, and a production process of the same.
The invention provides, in an aspect, a thin film magnetic head including: a lower core layer of a magnetic material; a gap layer of a nonmagnetic material formed on top of the lower core layer; a first insulation layer formed on top of the gap layer and having a first apex, the first apex being located on a surface facing a magnetic recording medium and defining a gap depth; a coil layer formed on the first insulation layer and being located at a first predetermined distance from the first apex; a second insulation layer laminated on the first insulation layer so as to cover the coil layer, the second insulation layer having a second apex, the second apex being located on the surface facing the magnetic recording medium at a second predetermined distance from the first apex; a third insulation layer formed on the first insulation layer in a bared area between the first and second apexes, the third insulation layer having an inclined plane sloping at a predetermined angle with respect to the top of the gap layer; and an upper core layer of a magnetic material having a tip region, a connecting portion and a body portion, the tip region being located on a surface facing the magnetic recording medium and establishing a magnetic gap via the gap layer, the body portion being formed on top of the second and third insulation layers and having a back end region being in contact with the lower core layer, and the connecting portion connecting between the tip region and the body portion, and being formed on top of the first and third insulation layers.
In the above thin film magnetic head, the predetermined angle of the inclined plane may preferably be in the range of 15xc2x0 to 50xc2x0.
The invention is also directed to a process for the production of a thin film magnetic head, the process including the steps of: forming a lower core layer from a magnetic material; forming a gap layer from a nonmagnetic material on top of the lower core layer; forming a first insulation layer on top of the gap layer, the first insulation layer having a first apex, the first apex being located on a surface facing a magnetic recording medium and defining a gap depth; forming a coil layer on top of the first insulation layer at a first predetermined distance from the first apex; forming a second insulation layer on top of the first insulation layer so as to cover the coil layer, the second insulation layer having a second apex, the second apex being located on a surface facing the magnetic recording medium at a second predetermined distance from the first apex; forming a third insulation layer on top of the first insulation layer in an area bared between the first and second apexes, the third insulation layer having an inclined plane sloping at a predetermined angle with respect to the top of the gap layer; and forming an upper core layer having a tip region, a connecting portion and a body portion from a magnetic material, the tip region being located on top of the gap layer on a surface facing the magnetic recording medium, the body portion being located on top of the second and third insulation layers with its back end region being in contact with the lower core layer, and the connecting portion connecting between the tip region and the body portion, and being located on the first and third insulation layers.
In the above process, the predetermined angle of the sloping region may preferably be in the range from 15xc2x0 to 50xc2x0.
Preferably, the upper core layer in the above process may be formed by the steps of: forming a primary coat from a magnetic material on top of the gap layer and the first, second and third insulation layers; forming a photoresist layer on top of the primary coat ;patterning the upper core layer by exposing the photoresist layer with light from above; removing exposed patterned areas of the photoresist layer; and forming the upper core layer from the magnetic material by frame plating using the photoresist layer.
The invention provides, in another aspect, a thin film magnetic head including: a lower core layer of a magnetic material; a gap layer of a nonmagnetic material formed on top of the lower core layer; a first insulation layer formed on top of the gap and having a first apex, a first sloping region and a first plane region, the first apex being located on a surface facing a magnetic recording medium and defining a gap depth, the first sloping region extending upward from the first apex, and the first plane region being connected to the first sloping region and being nearly parallel to the top of the gap layer; a first coil layer formed on top of the first plane region of the first insulation layer; a second insulation layer laminated on the first insulation layer so as to cover the first coil layer, the second insulation layer having a second apex, a second sloping region and a second plane region, the second apex being located on a surface facing the magnetic recording medium, the second sloping region extending upward from the second apex, and the second plane region being connected to the second sloping region and being nearly parallel to the gap layer; a second coil layer formed on top of the second plane region of the second insulation layer; a third insulation layer laminated on the second insulation layer so as to cover the second coil layer, the third insulation layer having a third apex and a third sloping region, the third apex being located on the second plane region on a surface facing the magnetic recording medium, and the third sloping region extending upward from the third apex; a first pocket region constituted by the second plane region and the third sloping region; and an upper core layer of a magnetic material formed on top of the gap layer and the first, second and third insulation layers, the upper core layer having a tip region and a back end region, the tip region being located on a surface facing to the magnetic recording medium, and establishing a magnetic gap via the gap layer, and the back end region being in contact with the lower core layer.
In the above-mentioned thin film magnetic head, the first pocket region is preferably filled with an insulative material to form a fourth insulation layer having a fourth sloping region.
Preferably, in the above thin film magnetic head, the second apex is formed on the first plane region, and a second pocket region is established by a bared area of the first plane region and the second sloping region.
In the aforementioned thin film magnetic head, the second pocket region is preferably filled with an insulative material to form a fifth insulation layer having a fifty sloping region.
The invention also relates to a process for the production of a thin film magnetic head, the process including the steps of: forming a lower core layer from a magnetic material; forming a gap layer from a nonmagnetic material on top of the lower core layer; forming a first insulation layer on top of the gap layer, the first insulation layer having a first apex, a first sloping region and a first plane region, the first apex being located on a surface facing a magnetic recording medium and defining a gap depth, the first sloping region extending upward from the first apex, and the first plane region being connected to the first sloping region and being nearly parallel to the top of the gap layer; forming a first coil layer on top of the first plane region of the first insulation layer; laminating a second insulation layer on top of the first insulation layer so as to cover the first coil layer, the second insulation layer having a second apex, a second sloping region and a second plane region, the second apex being located on a surface facing the magnetic recording medium, the second sloping region extending upward from the second apex, the second plane region being connected to the second sloping region and being nearly parallel to the top of the gap layer; forming a second coil layer on top of the second plane region of the second insulation layer; laminating a third insulation layer so as to cover the second coil layer, the third insulation layer having a third apex, a third sloping region and a third plane region, the third apex being located on the second plane region on a surface facing the magnetic recording medium, the third sloping region extending upward from the third apex, and the third plane region being connected to the third sloping region and being nearly parallel to the top of the gap layer; establishing a first pocket region by a bared area of the second plane region, and the third sloping region; forming a primary coat from a conductive material on top of the gap layer and the first, second and third insulation layers; forming a photoresist layer by coating a resist material onto the primary coat; patterning an upper core layer by photolithography of the photoresist layer; and forming a tip region and a body portion of the upper core layer from a magnetic material on top of the first, second and third insulation layer, the tip region being located on top of the gap layer, and the body portion being connected to the tip region and having a back end region being in contact with the lower core layer.